this lecture looked at the ventricles inside the brain, the dural sinuses outside the brain, the production of CSF, the different types of barriers present in the brain, and the flow of CSF through the ventricles and sinuses. dural sinuses are spaces in between inner and outer dural layers, either at the junction of dural sheets or above the dura. sinuses convey venous blood and as such have a sequence for draining which eventually leads into the internal jugular vein. the superior sagittal sinus drains into the confluence sinus, which drains into the transverse sinus, which drains into the sigmoid sinus, which drains into the jugular foramen, which drains into the internal jugular vein. the internal sagittal sinus drains into the straight sinus and joins the main drainage pathway at the confluence sinus. the cavernous sinus drains into the petrosal sinuses, which joins the main pathway at the transverse sinuses.
along with venous blood, CSF also eventually drains into these sinuses (or goes into the spinal cord). CSF is produced by choroidal epithelial cells which line the choroidal plexus, which surround cerebral arteries on the lining of ventricles. CSF is produced by these choroidal cells and secreted into the ventricles. CSF then flows through the ventricles: lateral to 3rd, 3rd to 4th (by way of the cerebral aqueduct), and then either into the spinal cord or into the subarachnoid space by the foramina of luschka or magendie. from there CSF ascends to the level of the sagittal sinus and exits the subarachnoid space by way of the arachnoid villi, which contain a membranous layer that allows CSF to flow into the sinuses. from there the CSF follows the drainage pathway of the venous blood as described above.
there are 3 unique barriers in the brain relating to blood and CSF. first is the blood brain barrier (see neurocranium part 2 for more detail). second is the blood / CSF layer-- which consists of choroidal epithelial cells. these cells contain tight junctions which does not allow the passage of larger molecules. third is the brain / CSF layer-- essentially the lining of the ventricles, made up of ependymal cells which are not joined by tight junctions. as such, they allow the passage of larger molecules, such as the metabolites of neurotransmitters, which can thus be detected in spinal taps (parkinson disease shows decreased catecholamines in CSF)
one last note: emissary veins transmit blood from the dural sinuses to below the scalp layer. just like venae comitantes, they aid in thermoregulation, in this case by routing the colder outer blood closer to the brain to cool it, or the opposite direction to warm it.
questions
sinuses and veins...
1. cerebral veins drain blood into...
2. what are dural sinuses?
3. where are dural sinuses located?
4. trace the pathway of venous blood from the superior sagittal sinus to the internal jugular vein.
5. trace the pathway of venous blood from the inferior sagittal sinus to the internal jugular vein.
6. trace the pathway of venous blood from the cavernous sinus to the internal jugular vein.
7. what does the cavernous sinus contain?
8. what are emissary veins?
9. how are emissary veins used for thermoregulation?
CSF...
10. where does CSF in the lateral ventricles eventually end up? describe the two possible pathways.
11. what is the choroid plexus? what does it do?
12. what is the brain/CSF barrier composed of? what does it let through?
13. what is the total volume of CSF in the body at any given time?
14. what is the pressure of CSF?
15. what is the total volume of CSF produced per day?
16. how does CSF move from the subarachnoid space to the sagittal sinus?
17. how does CSF support the integrity of the brain?
18. describe the equilibrium that exists between the epidural space and the subarachnoid space.
19. describe the brain/CSF barrier.
20. blockage of the CSF flow causes...
answers
1. dural sinuses.
2. spaces between periosteal and meningeal dural layers that convey venous blood.
3. at the junction of dural sheets or above the dura.
4. superior sagittal sinus -> confluence sinus -> transverse sinus -> sigmoid sinus -> jugular foramen -> internal jugular vein.
5. inferior sagittal sinus -> straight sinus -> confluence sinus -> transverse sinus -> sigmoid sinus -> jugular foramen -> internal jugular vein.
6. cavernous sinus -> petrosal sinuses -> transverse sinus -> sigmoid sinus -> jugular foramen -> internal jugular vein.
7. cranial nerves: IV, V1,V2,V3, VI, and internal carotid artery
8. veins that allow for transport of venous blood between the scalp and the dural sinuses.
9. emissary veins help maintain the temperature of the brain by routing colder blood from the surface of the scalp closer to the brain during hyperthermia and the opposite motion during hypothermia.
10. travels from the lateral ventricle to the 3rd ventricle, through the cerebral aqueduct into the 4th ventricle. at this point it can flow downward into the spinal cord, or through the foramina of luschka and magendie into the subarachnoid space-- and from there into the superior sagittal sinus.
11. the choroid plexus surrounds cerebral arteries and secretes CSF into the ventricles.
12. made of choroid epithelial cells which are joined by tight junctions-- preventing the flow of large molecules.
13. 150mL
14. 10mm Hg
15. 450mL
16. through arachnoid villi, protrusions of the arachnoid layer that have a filtering membrane that allows CSF to pass into the sagittal sinus.
17. by being suspended in CSF, the brain is protected in three ways: the mass (~1400g) is effectively reduced to 40g due to buoyancy. the cranial nerves and veins are protected. lastly, arachnoid trabeculae serve to anchor the brain in place.
18. there is an equilibrium between the pressure of venous blood in the epidural space and the CSF in the subarachnoid space.
19. the brain CSF barrier is made up of ependymal cells which are not joined by tight junctions; hence fluid and larger molecules can flow readily-- this allows metabolites of neurotransmitters, for example, to be present in CSF in ventricles.
20. hydroencephaly
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